Coating metal



Patented Feb. 10, 1931 UNITED STATES PATENT OFFICE VAN M. DARSEY, OF DETROIT, MICHIGAN, ASSIGNOR TO PARKER- RUST-PROOF COM- PANY, OE DETROIT, MICHIGAN, A. CORPORATION OF MICHIGAN COATING METAL No Drawing.

This invention relates to coating metal, and more particularly to treatment in con nection with coating iron or steel with phosphates.

It has been a common practice for some years'to boil iron or steel articles in a dilute solution of phosphoric acid, or phosphates, and thereby coat the surface with a comparatively insoluble coating of phosphates. Re-

m cently it has been discovered that the addi tion of a compound of copper to the solution greatly increases the rapidity with which the phosphate coating is deposited, but at the same time metallic copper is deposited, in-

]5 terspersed through the phosphate coating.

The coating with copper interspersed therethrough is suitable to form a base for paint, enamel or the like, but does not of itself form a satisfactory rustproofing. Prob- 0 ably the rusting of the iron is accelerated by the electric action due to the copper adjacent thereto.

It is one purpose of this invention to treat such a phosphate and copper coating so as to greatly increase its resistance to rusting.

Articles coated with a phosphate and copper coating dipped in a hot solution of potassium chromate for a brief period resist rusting about as well as similar articles coated so with the phosphate coating without the copper, and the phosphate and copper treatment and subsequent treatment with the chromate solution requires much less time than the formation of the coating of phosphates alone.

The chromate solution has no visible or chemically ascertainable effect upon either the phosphate coating or the copper, but probably it affects the electrical action of the copper. At any rate, it very markedly re- 4 tards the rusting of the articles treated.

The preferred strength of the chromate solution is from 1 to 5 grams per liter of water, but the strength of the solution may be even more widely varied without injurious 46 results. The strength of the solution does Application filed May 13, 1929. Serial No. 362,873.

not have any marked efiect on the result. A cold solution has a similar effect but acts much more slowly than the hot solution.

Potassium dichromate maybe used also, and other soluble chromates and dichromates may be employed, if preferred. Chromic acid (CrO may be employed instead of the chromates,- but care must be taken not to use too strong a solution. A solution of two or three grams to a liter of water works fairly well, but over three grams to the liter perceptibly injures the phosphate coating. For this reason a chromate solution is preferred to a chromic acid solution.

It is sometimes desirable to reduce the amount of copper deposited in the coating. Dipping the articles in a hot chromate solution before placing them in the phosphate and copper bath retards the deposition of copper while at the same time it reduces the time in which the reaction of'the bath with the articles is completed. Preliminary dipping in a chromic acid solution likewise retards the deposition of copper, but it retards the formation of the phosphate coating, instead of accelerating it, as the chromate solution does.

lVhen a soluble salt of lead is added to a phosphate coating bath, lead is not deposited to any appreciable extent in the absence of some other added material; but when a little soluble salt of copper is added, the lead is deposited very rapidly, and forms with phosphates a somewhat soft and smudgy coating. Treatment of the articles in a chromate solution before subjecting them to the phosphatelead-copper bat-h retards the deposition of the lead and improves the coating. Treatment of the thus coated articles with a chromate or chromic acid solution improves its rustresisting qualities. The chromic acid solution for the coating containing lead is more desirable than with a coating containing co per, but free from lead, as lead forms a su stantially insoluble chromate.

While the phosphate coatings mentioned above as being benefited by treatment with a chromate solution were only those containing copper or lead, it will be understood that phosphate coatings containing other metals having a different electric potential from iron may be rendered more rust-resistant by treatment in a solution containing a soluble chromate or chromic acid, and that treatment of iron or steel with a solution containing the chromic acid radical before treatment in a phosphate bath retards the deposition on the iron of other metals which are less basic than iron and which are dissolved in the phosphate bath.

From the above, the nature of the invention and the manner of its use will be apparent to those skilled in the art.

What is claimed is:

1. The method which consists in treating an article having a surface ofiron or steel bearing a phosphate coating containing a metal having a potential different from that of iron or steel, witha solution of a material containing the chromic acid radical.

2. The method which consists'in treating an article having a surface of iron or steel bearing a phosphate coating containing a metal having a potential different from that of the iron or steel, with a solution of a salt of chromic acid.

3. The method which consists in treating an article having a surface of iron or steel bearing a phosphate coating containing a metal with a potential different from that of the iron or steel of said surface, with a hot dilute solution of a material containing the chromic acid radical.

4 The method which consists in treating an article having a surface of iron or steel bearing a phosphate coating containing a metal with a potential different from that of the iron or steel of said surface, with a hot solution of a salt of chromic acid.

5. The method which consists in treating an article having a surface of iron or steel bearing a phosphate coating containing a metal less basic than iron, with a solution of a material containing the chromic acid radical.

6. The method which consists in treating an article having a surface of iron or steel 9. The method which consists in treatin an article having a surface of iron or stee bearing a phosphate coating containing a metal with a. potential different from that of the iron or steel of said surface, with a hot diluite solution of an alkali salt of chromic ac1 10. The method which consists in treatin with a solution containing the chromic aci radical an article having a surface of iron or steel, immersing the treated article in a dilut phosphate solution containin in solution a etal less basic than iron and thereby coating said surface with a phosphate coating containing said metal less basic than iron, and treating the coated surface with a solution containin the chromic acid radical.

11. The method which consists in treating with a solution of a salt of chromic acid an article having a surface of iron or steel, immersing the treated article in a dilute phosphate solution containing in solution a metal less basic than iron and thereby coating said surface with a phosphate coating containing said metal less basic than iron, and treating the coated surface with a solution of a salt of chromic acid.

12. The method which consists in treating with a solution of a salt of chromic acid an article having a surface of iron or steel, immersing the article in a hot dilute phosphate solution containing a soluble compound of copper, until a phosphate and copper coating is formed on said surface, and treatin the coated surface with a solution of a sa t of chromic acid.

13. The method which consists in treatin an article having a surface of iron or stee with a hot dilute solution of alkali chromate, immersing the treated article in a hot dilute phosphate solution containing co per in solution, until said surface is coate with copper and phosphate, and treating the coated surface with a hot dilute solution of alkali chromate.

14. The method which consists in treatin with a solution containing the chromic aci radical an article having a surface of iron or steel, and immersing the treated article in a dilute phosphate solution containing in solution a metal less basic than iron and thereby coating said surface with a hosphate coating containing said metal less Basic than iron.

15. The method which consists in treating with a hot dilute solution of alkali chromate an article having a surface of iron or steel and immersing the treated article in a hot dilute phosphate solution containing a soluble VAN- M. DARSEY. 

